1. Field of the Invention
The present invention relates to a lens system for a video projector, and more particularly to a refractive type lens system located in front of a cathode ray tube for projecting onto a screen a video image formed on a face plate of the cathode ray tube.
2. Description of the Prior Art
Recently, various types of lens systems have been provided with the development of video projectors. The various types of lens systems are designed for complying with the request for providing higher performance of the lens system, larger aperture thereof, or a wider angle of view thereof, respectively. Furthermore, a new technique called "optical coupling", in which a space formed between the cathode ray tube and the lens system is filled with a proper material, is suggested for cooling the space or for decreasing the reflection caused on the optical surfaces therebetween. Thus, a plurality of designs of the video projector lens systems have been proposed for matching the new technique.